[Is the correlation between adequate dialysis in peritoneal dialysis and nutritional parameters mathematical or biological? Influence of residual renal function and comorbidity].

The relationship between urea Kt/V and nPCR (nPNA) is partly due to a mathematical coupling and greatly depends on the residual renal function (RRF). On the other hand, albumin could be just a comorbidity marker. Our objective in this study was to verify whether dialysis dose in peritoneal dialysis (PD) is biologically related to the nutritional state measured by the mean values of several parameters not mathematically related while analyzing the influence of RRF and comorbidity (C). 101 stable PD patients, 60M and 41F with a mean age of 59.3 +/- 14.3 years, were studied and followed up every six months for a mean time of 35.8 +/- 22.3 months (8-112). The variables studied were initial comorbidity, plasma albumin, normalized protein nitrogen appearance (nPNA), lean body weight % (LBW%) and fat-free mass index (FFMI) derived from creatinine, and RRF. In every study (n = 471) the 24 hours dialysate and urine volumes were collected and the total (T), dialytic (P) and renal (R) urea KT/V and normalized creatinine clearance (CCR) were determined and compared with the nutritional parameters. When starting PD 48 patients (47.5%) had some C and 34 (33.7%) were already anuric. The correlations of nPNA with T-KT/V and T-CCR (n = 101) were r = 0.67 and 0.50 (p < 0.0005) while the correlations of LBW% with T-KT/V and T-CCR were r = 0.36 and 0.40 (p < 0.0005) respectively. The correlations of albumin with T, P and R KT/V and CCR did not reach significance. The nutritional state was better in patients with a higher RRF and albumin showed significant differences when related to morbidity. KT/V and CCR correlations with nutritional variables not mathematically related verify the hypothesis that dialysis dose is biologically associated with the nutritional state.